1. Field of the Invention
The present invention relates to a wafer structure. More particularly, the present invention relates to a direct contact through hole type wafer structure.
1. Description of the Related Art
A trend for electrical products is to be light, short, small and thin. Not only the chips manufacturing technology but also the packaging technology is developed rapidly to meet the trend. Since a width of a chip is reduced quickly, an integration of the chip is increased and a volume of a chip is decreased. As a result, it is an important task to develop a new packaging technology, which is able to form a small volume package.
Memory modules, for example, are the common semiconductor products. The memory modules are generally formed by the following steps. Chips are first packaged, and then the packages are attached to a printed circuit board. The steps of forming the memory modules are complicated and manufacturing costs are high. Additionally, the arrangement of the packages on the printed circuit board is two-dimensional. An area occupied by the packages is large, so that the packaging density is low. To further reduce reduction of a size of the memory module is limited.
A stacked-type package structure is designed to overcome the above problems. The package structure is three-dimensional, thus an area occupied by packages is reduced and the packaging density is increased.
FIG. 1 is a schematic, cross-sectional diagram of a conventional stacked-type package structure.
Referring to FIG. 1, chips 10a, 10b and 10c are coupled with leadframes 14a, 14b and 14c by bonding wires 12, respectively. The chips 10a, 10b, 10c and the leadframes 14a, 14b, 14c are sealed by epoxy 16 to form packages 18a, 18b and 18c. The packages 18a, 18b, 18c are stacked and coupled with each other by outer leads of the leadframes 14a, 14b, 14c. Outer lads of the leadframe 14c couple with contacts 22 on a printed circuit board 20 by tape automatic bonding.
Although the stacked-type package structure reduces the area occupied by the packages, a height of the stacked-type package structure is high. Furthermore, a signal-transmitting path from the stacked-type package structure to the printed circuit board is long, so that electrical impedance is increased. As a result, signals transmitted decay and are delayed.